I would like to animate a set of text, like this http://www.doctorhugo.org/e-poetry/shewalks.gif as in the the gif i create should consist of text I choose. Are there any tools for that? How would I approach it in HTML5/canvas?
It's called 'ASCII Art'. Google 'ASCII Art Generator' and you'll find plenty of examples. You'll need some animated images to use as the source to then convert to ASCII.
Once you have it converted to ASCII, you could place each 'frame' of text in a DIV with a monospaced font and then, via JS, rotate showing each DIV one-by-one to create the animation.